Download Crop Module: Garlic - Red Tractor Assurance

The disease initially infects roots and spreads back into
the bulb causing destruction of tissue from the base
upwards. This destruction is accompanied by a white
cotton wool-like fungal growth. Early infection causes
bulbs to completely rot in the field and later infections
cause the total collapse of bulbs in store. Progress of
infection is checked at the initial drying stage (28-30°C)
but continues when the store is cooled.
There is development of control measures but it is
therefore essential to:
Note infection areas on farm maps and not only avoid
such areas but also where possible avoid spreading
contaminated soil to other parts of the farm, particularly
with cultivation equipment.
Monitor crops to ensure that any occurrence of infection
is recorded. Premature yellowing of foliage in patches is
the most usual indicator.
Make every attempt to avoid harvest of infected bulbs.
Field population of resting spores (sclerotia) can be
reduced by hand collection of infected bulbs but this
is recommended only for small areas where such action
is practical.
EAMU for use of Folicur (tebuconazole) and Signum
(boscalid + pyraclostrobin). Both Folicur and Signum if
applied early will give some control of field infections.
Fusarium base rot (Fusarium culmorum f.sp. cepae)
Basal rot of garlic is caused by Fusarium culmorum.
Soilborne inoculum infects garlic through the stem plate
rather than through roots or storage leaves. Leaves of
infected plants may not produce disease symptoms, but
can be a source of the disease. Transmission can occur
when infested soil or debris is transported on equipment,
seed, or runoff water. The fungus can survive indefinitely
in the soil. Fusarium culmorum can also infect elephant
garlic, but not to the same degree as garlic. Onion is not a
host. Symptoms include pre-emergence decay of cloves
and seedlings. Stem plates and storage leaves may
decay in the field during the growing season. Lesions
may have a reddish fringe. Disease expression is erratic
from year to year and field to field. Post-harvest decay
may involve a single clove or the entire bulb.
Cultural Control: Growers commonly rotate garlic with
non-host plants to reduce disease pressure. Cereals are
a host of garlic strains of Fusarium culmorum. Growers
also avoid planting in fields with a history of basal rot
problems. The primary cultural control of basal rot is
curing bulbs properly before storage and storing the
garlic at cool temperatures, as F. culmorum is favoured
by warm conditions. Fields with good drainage and
freedom from sub-surface pans (or compaction) will
minimise problems. There are no chemical treatments.
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Downy mildew (Peronospora destructor)
Downy mildew is a serious foliar disease that commonly
requires routine treatment. The disease is readily spread
by air-borne spores and encouraged by warm humid
conditions, closely following the infection criteria of
potato blight.
Maintaining 500m separation between overwinter
(most susceptible) and spring crops will minimise
cross-infection.
Infected crop debris should be ploughed in as soon as
possible after harvest to minimise any carryover.
Use of weather based prediction models is anticipated in
the near future.
Treatment should be based on routine monitoring so that
infection can be identified at an early stage. Following
this, a routine spray programme is necessary to ensure
adequate control using currently approved fungicides. It
is recommended to alternate chemical groups to avoid
the risk of resistant strains developing.
Leaf Blight (Botrytis squamosa)
Leaf spot is a disease that affects the foliage in cool wet
conditions. It most seriously affects either seedlings of
overwintered varieties in the autumn or the foliage of
spring-planted varieties, particularly closer to harvest.
This disease will require treatment in occasional seasons
only. The risk of infection increases with increasing
crop density.
Development work is in progress to predict infection
conditions (as with downy mildew).
Treatment is usually combined with downy mildew control
in overall fungicide programmes and should be based on
routine monitoring. Disease incidence is more tolerable
than downy mildew since the disease is less progressive
and less likely to cause serious crop loss.
Garlic foliage becomes more susceptible to infection
as harvest approaches and as the density of the crop
canopy increases. Early infection of the outer leaves can
affect skin retention in store.
Leaf blotch (Cladosporium allii-cepae)
Leaf blotch is a disease that occurs when the combination
of temperature and long periods of leaf wetness allows
germination and penetration of the fungus. In such years
infection can result in complete defoliation. Symptoms
are bleached elliptical eyespots on the leaves that spread
parallel to the leaf veins and can destroy entire leaves.
Routine control measures for this disease are not
normally necessary.
Red Tractor Assurance for Farms – Crop-specific Module: Garlic
© Assured Food Standards 2015